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Geophysics Department Seminar - Knut Christianson: Stability of Thwaites Glacier, West Antarctica from 3D Radar Tomographic Mapping
Thwaites Glacier poses perhaps a singular threat to the stability of the West Antarctic Ice Sheet. Recent model convergence indicates that marine ice-sheet collapse triggered as a result of Thwaites Glacier retreat is inevitable or already occurring. Despite several “high” resolution mappings by numerous modern aerogeophysical platforms, the bed topography and conditions of Thwaites Glaciers remain undersampled. Thus, models rely on inversions of basal conditions from surface velocities and/or ice-sheet geometry. Most models reveal a similar structure: the current grounding line of the glacier sits on an area of rough and elevated topography that is likely associated with high basal shear stress.
Beyond this current grounding-line sill, there are only two prominent ridges in basal shear stress that could temporarily halt retreat for decades to centuries; here we investigate the nature of those ridges, which are likely controlled by both subglacial topography and bed conditions. Retreat rate will depend on both the topography and character of the bed with consequences for inland stress transmission and thus also future glacier evolution. The nature of these ridges and their underlying geology was uncertain due to previous limitations in geophysical mapping technologies. We use airborne 3-dimensional radar tomography to map out the subglacial topography over these ridges in basal shear stress at unprecedented resolution (25-m grid posting in the along- and across-track directions), and interpret our results using complimentary active-source seismic data that better elucidate basal conditions. Our data show a heterogenous bed, indicating the need to use spatially variable basal friction treatments in ice-sheet models.